Antennas are important elements in wireless communication devices, such as mobile phones and personal digital assistants. To communicate in multi-band communication systems, a bandwidth of an antenna in the wireless communication device needs to be wide enough to cover multiple frequency bands, especially a low frequency part needs to cover 700-900 MHz. In addition, because the wireless communication device trends to a maximization screen and a lightweight size, it is generally desirable to use one antenna to support all frequency bands to save cost. Therefore, how to use a single antenna structure to support all the frequency bands is an important topic of antenna design.